Halide treatment and circulation in aluminum refining system



1955 N. w. F. PHILLIPS ETAL 3,216,820

HALIDE TREATMENT AND CIRCULATION IN ALUMINUM REFINING SYSTEM 2 Sheets-Sheet 1 Filed June 4, 1962 mum/0m Norman W F Phi/Ups mmmzmozOu Frederic/r Will/0m Sou/ham mwmomzoomo wmamE.

Af/omey United States Patent 6 3,216,820 HALIDE TREATMENT AND CIRCULATKON IN ALUMINUM REFINING SYSTEM Norman W. F. Phillips and Frederick William Southam,

Arvida, Quebec, Canada, assigiors to Aluminium Laboratories Limited, Montreal, Quebec, Canada, a corporation of Canada Filed June 4, 1962, Ser. No. 199,934 16 Claims. (CI. 75-68) This invention is concerned with the refining of aluminum metal by so-called subhalide distillation where gaseous normal aluminum halide is employed to convert aluminum metal, from an impure body thereof, to gaseous aluminum subhalide which is thereafter decomposed to yield purified metal and a restored quantity of the normal halide. In particular, the invention is related to procedure and apparatus for treating and recirculating the halidecontaining gas in the subhalide refining system, whereby effectiveness of the operation is promoted, as to re-use of the gas with high efiiciency in or for the principal reactions, and also as to improved operation of the converter unit Where the aluminum is reactively separated from the impurities.

In the subhalide process for refining or extracting aluminum, the impure material generally consists of alloys of aluminum with other metals or the like, or other compositions or bodies of aluminum and foreign material, usually metallic, all such mixtures, compositions or aggregates being here generically considered as impure aluminum. In a preferred way of carrying out the refining operation, the impure material, in divided solid form, is supplied substantially continuously, e.g. by increments from time to time, into a suitable converter of furnacelike character, where it is heated and where the normal halide of aluminum in gaseous form is passed through it, for example aluminum trichloride (AlCl or aluminum tribromide (AlBr also commonly called aluminum chloride and aluminum bromide. At appropriate temperature, ordinarily in the range of about 1000 C. and upwards, the gaseous halide reacts with the aluminum in the material to produce, in gaseous form, an aluminum subhalide, e.g. monohalide. Thus the conversion reaction, where the treating gas is aluminum trichloride, yields aluminum monochloride, carrying the aluminum in gaseous combined form.

The solid material under treatment is thus progressively depleted of aluminum, e.g. as it moves downward through a converter of vertical type, so that the resulting aluminum-impoverished solids are discharged from the lower part of the converter. The gas withdrawn from the upper part of the conversion chamber contains the aluminum subhalide, usually together with unreacted normal halide, and is advanced to the decomposer where at suitably lower temperatures the reverse reaction occurs, with the subhalide reverting to aluminum and normal alumi num halide. The metallic aluminum, conveniently in molten state, is there deposited and collected, while the discharged gas now again consists essentially of the normal aluminum halide, e.g. aluminum trichloride.

It has been apparent that efiiciency would be served by recirculating the gaseous normal halide from the decomposer to the converter, where it can be reused in the same manner, the circulation system advantageously including some heating means so that the halide is of an appropriately high temperature, e.g. at or approaching that of the conversion reaction, for efiiciency of space and time in the operation of the converter. It has been found, however, that circulating gas in a monochloride refining system tends to become contaminated or diluted with non-reacting gas, i.e. gas which is inert or of no use in the desired reactions. Such gas appears chiefly to be derived from materials introduced into the system, es-

pecially the charge of impure aluminum, although leakage or other fortuitous circumstances may also contribute to the dilution of the halide stream. Primarily, the nonreacting gas appears to consist chiefly of hydrogen, methane, and the like, formed from traces of moisture carried into the apparatus with the raw material (e.g. the aluminum alloy or other impure aluminum under treatment), and from carbon in such material or in the apparatus. As such gas builds up, the effectiveness or efliciency of the operations are lowered, so that it is desirable to provide for removal of the gaseous contamination.

It has been found, pursuant to another invention, that an effective way of preventing such buildup of undesired gases is to condense a portion of the circulating normal halide to non-gaseous state while removing the non-condensable gas from the portion thus treated. It has been further found that the content of diluent gas in the circulating system can in general be kept to a desirable minimum by such condensation and separating action upon a relatively minor part of the circulating stream; the amounts of so-called permanent gas thus removed, although small, are ordinarily at least as large as the progressive increments coming into the stream from the charge in the converter or otherwise. It will be understood, however, that the proportion of halide subjected to condensation, with corresponding removal of noncondensables, will generally determine the circulating load of such non-condensable material in the system, and such proportion may therefore be selected, for any system, to achieve the desired limitation on the presence of nonreacting gas.

The condensed halide, e.g. aluminum trichloride, is then re-evaporated, after other gases have been separated from it, to provide a reconstituted or auxiliary supply of gaseous halide, which is then continuously returned to the circulating system.

In accordance with a special feature of the present invention, the evaporation of the condensed aluminum chloride or the like is advantageously effectuated with another portion of heated halide gas from the circulating system. The resulting heat exchange in the volatilization of the halide thus yields bodies of gaseous halide, or a combined gaseous halide fiow, which has a relatively low temperature. This low temperature gas may be conveniently supplied to the converter at the locality where spent charge material is removed, so that the latter material is cooled for convenience in handling while the temperature of this usually minor stream of halide is correspondingly and economically raised before it joins the main flow of such gas in the zones of principal reaction.

In addition to the supply of halide gas which is only mildly heated, to the residue discharge region of the converter, and by way of supplement to the main stream of gaseous halide supplied at the lower part of the reaction zone, another stream of the halide gas at an intermediate temperature can advantageously be introduced at a locality between the discharge point and the inlet of the main gaseous fiow. Such supplemental feed of the normal halide, e.g. aluminum trichloride, can be diverted from the principal circulating line or conduit upstream of the heater, so that it in effect carries the temperature at which it was discharged from the decomposer. This intermediate gas feed provides additional heat exchange with the essentially depleted charge material, raising the temperature of such gas toward the reaction value, while initiating the cooling of the residue upstream, so to speak, of the final cooling by the lowest temperature gas.

While elements of apparatus for the system may involve any of a variety of forms and while the condensing stage may provide for deposit of the halide, viz. aluminum chloride, in liquid form, as in a molten salt carrier consisting of a mixture of sodium and aluminum chlorides, and while the evaporation step may be effected from a similar molten bath which is maintained at temperature by heat exchange with hot gas from the main stream and which is supplied with the trichloride in either solid or salt-carried liquid form, a further feature of the invention, involving special utility and convenience, embraces the condensation of the normal halide as a divided solid, e.g. powder, which is then flash evaporated by directing it into a stream of the relatively hot gaseous halide. A rapid continuous operation is thus easily achieved, while supplemental materials or special heat exchange structures are not needed.

Indeed the procedure and apparatus for evaporation of solid aluminum trichloride by contact with heated gas, e.g. gaseous aluminum trichloride, as sometimes herein called flash evaporation, represents a specific feature of invention, having special advantages. These advantages include not only the novel coaction of the flash evaporation in the foregoing process with respect to purification and re-use of circulating aluminum trichloride in the aluminum-refining circuit, but also extend to the action of converting aluminum trichloride to a gaseous form under various circumstances, for instance in providing initial or continuing flash supply of such trichloride for monochloride distillation or the like. As will be explained more fully below, the arrangement of bringing pulverulent aluminum trichloride into contact with a stream of heated gaseous aluminum trichloride yields rapid and complete evaporation while avoiding difficulties heretofore encountered in attempts to evaporate this compound, especially by sublimation, it being understood that aluminum trichloride, at atmospheric pressure, passes directly between solid and gaseous states.

In the accompanying drawings, which are illustrative of the procedure and apparatus of the invention:

FIG. 1 is a diagrammatic and somewhat simplified view of one example of a system for refining aluminum by the monochloride process, including the described features of improvement;

FIG. 2 shows an evaporating system for aluminum trichloride, including an evaporator set forth in vertical section (structurally simplified for purposes of illustration), suitable for employment in the process of FIG. 1, but here shown as included in a diagrammatic heating circuit for independent generation of aluminum trichloride gas;

FIG. 3 is a horizontal section on line 3-3 of FIG. 2;

FIG. 4 is an enlarged fragmentary vertical section showing a modified form of gas distributor, as at the lower part of the evaporator in FIG. 2; and

FIG. 5 is a horizontal section on line 5-5 of FIG. 4.

Referring to FIG. 1, the converter 10 is shown as an upright, generally cylindrical, furnace-like structure, which is lined or walled with refractory material and which has an inner chamber 11 kept substantially well filled with charge material 12 introduced in successive increments through a suitable lock device 13 at the top. While other apparatus for effecting the conversion reaction, arranged to handle the impure metal in solid or liquid form, may be employed, the illustrated structure is most advantageously of the type shown and described in United States Patent No. 2,937,082, granted May 17, 1960 on application of A. H. Johnston et al., which is designed to receive a charge of the impure alloy in lump, fragment or granular form.

A pair of annular graphite electrodes 15, 16, vertically spaced at the reaction zone 17, provide for the supply of heat by electrical resistance heating through the charge, under appropriate current conducted to the electrodes. Immediately below the reacting region, the main stream of preheated normal halide gas is introduced from a conduit 18, to rise upwardly through the charge where the desired conversion reaction occurs, removing aluminum metal in the compound form of subhalide, e.g. aluminum monochloride, which then passes out at the upper part of the converter, together with unreacted trichloride, through the conduit 20.

Appropriate means are provided at the bottom of the converter chamber for discharge of spent residue, i.e. solid material largely depleted of aluminum. As an example of such means, a cone-shaped agitator and extractor 21, having a vertical axis, is mounted to turn slowly on a vertical shaft 22 having appropriate driving means 23. The spent solids are thus aided in discharge through a chute 24 and appropriate locking devices 25.

As explained above, it is highly desirable to bring the temperature of the solid material to a relatively low point from the reaction temperatures that are usually well above 1000 C. Initial cooling is effected by introducing a stream of intermediate-temperature gas through a conduit 27 at a locality spaced below the main gas inlet 18, while the final or principal cooling operation is achieved with lower temperature gas supplied through a pipe 28 and the hollow tubular interior 29 of the shaft 22, for release, via a suitable manifold system 30, through the upward conical surface of the extractor device 21, e.g. at a plurality of localities distributed over the latter. In this fashion the extractor device itself, usually made of iron, steel or other metal, is kept at a relatively low temperature, say below 500 C., to avoid its deterioration, while very significant cooling is effected of the fragments or granules of charge residue that are moved or tumbled about on the extractor and that rest in the body of such material, above the extractor.

In the system shown, the product gas from the converter, through the conduit 20, traverses the decomposer 32, where with the aid of appropriate cooling to reduce the temperature, the dissociating subhalide, e.g. aluminum monochloride, is 'reactively decomposed to yield purified aluminum metal and reconstituted normal halide, viz. aluminum trichloride. The aluminum is thus condensed, so to speak, in molten form on the baffles or other condensing structure or medium of the decomposer, to collect and discharge from the bottom of the device, while the gas, now consisting essentially of aluminum trichloride, at a reduced but moderately high temperature, is withdrawn through a further conduit 34.

For re-use of the halide gas it is advanced by a suitable circulator or pump 35, especially to make up for pressure losses in the system; that is to say, the circulator, which may be in the nature of a pump having appropriate corrosion-resisting elements, compresses the gas sufficiently to overcome the pressure drop in the complete path of circulation.

By and from the circulator, the gas advancing through conduit 36 traverses a heater 38, e.g. containing an electrically heated bed of carbon or the like (not shown), which preheats the gaseous trichloride to a high temperature, for the principal supply, through conduit 18, to the converter.

In accordance with the present invention, a supplemental pipe 45 leads a minor proportion of the trichloride gas from the main circulating line, conveniently upstream of the circulator 35, to a condenser 42, which may be of any suitable type, for example as shown and described in United States Patent No. 2,883,162, granted April 21, 1959 on the application of Bryan Rapson. The aluminum trichloride is condensed in solid form, under the action of appropriate cooling means (not shown) to discharge as a powder or the like through a duct 43, while noncondensable gases, being a portion of the contaminating or diluent gas of so-called permanent character in the circulating stream, are discharged from the condenser through a pipe 44, thereby separating such contamination or diluent from the system.

The condensed aluminum trichloride powder is restored to the gaseous state in the fiash evaporator 45. A

stream of the moderately high temperature trichloride gas, preferably withdrawn from the main system at a locality downstream of the circulator, is supplied through a pipe 46, to be projected upwardly, from the bottom of the evaporator chamber, by the nozzle 47. The aluminum trichloride powder from the duct 43 is fed directly into the stream of heated trichloride gas, as by a screw feeder 48. Essentially instantaneous evaporation occurs, so that gaseous aluminum trichloride, derived both from the volatilized powder and the stream of the nozzle 47, is discharged into the pipe 28 and thus conducted to the cone extractor 21 as described above. This gas, though still at elevated temperature, is usually only slightly above the evaporation point of the trichloride, and is thus relatively cool with respect to other conditions in the system.

If additional or make-up halide is needed, a convenient way of supplying it is by a supplemental screw feeder 49, arranged to deposit such additional aluminum trichloride, for example, into the duct 43, so that it can be evaporated in the device 45 along with the condensed material that is to be recirculated.

The supplemental stream of intermediate temperature gas, advanced through the conduit 27, is conveniently withdrawn from the main recirculating conduit 36 at a locality downstream of the circulator but upstream of the heater 38, e.g. at the same place as the withdrawal of gas for the evaporator through pipe 46.

As will be understood, conditions in the system may vary in accordance with requirements of operation. In general, the temperature in the converter is preferably kept at a value of 1000 C. and upwards, most advantageously above 1200 C. The pressure may be subatmospheric, although convenient operation can be achieved at higher pressures, especially at or near atmospheric pressure. The gas leaving the decomposer is usualy at a temperature upwards of 600 C., more likely 700 C. or somewhat above, especially where the aluminum is deposited in liquid, i.e. molten, form in the device 32. The minor flows of gas supplied to the condenser, and to the evaporator, and likewise to the pipe 27, are essentially at the same temperature as on leaving the decomposer, e.g. in a range of 600 C. to 800 C. or so. The cooler flow of trichloride gas through the pipe 28, derived from the evaporator, is usually at a temperature not higher than about 400 C., and most advantageously at 300 C., the minimum being the evaporating point of the trichloride at the pressure prevailing in the system.

By way of example of operation, it will be assumed that the system is functioning at a capacity of approximately three tons per hour of aluminum product, e.g. in the discharge from the decomposer 32. Operation is also assumed at approximately atmospheric pressure. With the charge to the converter consisting of an alloy containing approximately aluminum, residue is withdrawn at the bottom, through the duct 24, in amount of approximately 5700 pounds per hour. The mass in the reaction zone is kept at a temperature of about 1300 C., yielding aluminum monochloride gas, along with unreacted trichloride, for passage to the decomposer for the desired production of pure aluminum. The total circulating gas load in the system is of the order of 600,000 cubic feet per hour, or slightly more, such gas, when consisting essentially of aluminum trichloride, having a density of about 0.1 pound per cubic foot. The circulator 35 accordingly handles a flow of the magnitude just stated.

The gas in the line 34 from the decomposer has a temperature of 700 C., and approximately 2% of it is withdrawn through the line 40 to the condenser 42, i.e. so as to condense approximately 2% of the recirculating trichloride, or 1200 pounds per hour. For the action of the evaporator 1200 pounds per hour of trichloride gas at 700 C. is introduced through the nozzle 47 so that the cooling supply into the extractor cone 21 constitutes about 2400 pounds per hour of gaseous aluminum trichloride at 300 C. The depleted charge material just above the cone is thus brought down to about 500 C. in temperature, having traversed a region at 700 C., where the supplemental flow, at such temperature, is introduced from the line 27, the latter being in the amount of 4600 pounds per hour (of aluminum trichloride). The heater 38 raises the temperature of the main stream of gas to about 1200 C. or a value in the range of 1200 C. to 1300 C., for entry into the converter conduit 18.

As will now be seen, the procedure and apparatus afford an effective way of recirculating the trichloride gas, while also affording provision for depletion of contaminating or diluent gas so as to avoid undesirable build-up of the latter. At the same time provision is efficiently made for utilization of all trichloride, and especially for desired cooling and heat exchange functions in the operation of the converter. As explained, the minor flow of halide gas through the supplemental condensing and evaporating circuit need ordinarily be only a small proportion of the total circulating halide, e.g. from 1% to 10%.

Referring now to FIGS. 2 and 3, these views illustrate a flash evaporator, i.e. as to essential structural features of a practical example of such device, the evaporator being suitable for use as the device 45 of FIG. 1, but here shown, for variety of illustration, as arranged with a circuit so as to include separate heating means, for independent generation of a stream of aluminum trichloride gas.

It may be explained that sublimation of a powder, such as aluminum trichloride, to yield the compound in gaseous state is a difiicult operation by conventional methods or equipment because of the relatively poor heat transfer that is obtainable to substances in powder form, e.g. in cases where a powder must engage a heated surface. In addition, aluminum chloride is very hygroscopic, so that by reason of unavoidable traces of moisture, oxide residue forms on heating surfaces and causes large thermal resistance. Because of the thermal conduction problems and surface oxidation difliculties in the situation of aluminum trichloride, elforts to evaporate this compound from the solid state have not usually been very successful, yet it would nevertheless be desirable to utilize such material in its conventional solid form and without special conditions of pressure.

It has been found that aluminum trichloride as a gas can be efficiently heated by suitable means, and the present improvements are predicated on the discovery of procedure whereby heated aluminum trichloride gas can be utilized for evaporation of cold trichloride powder. The evaporation is efficient, i.e. in transfer of the heat vaporization to the aluminum trichloride, and traces of oxide (alumina) may form without affecting efliciency. The supply of heat from a suitable source is directed to a flow of trichloride gas, rather than to the solid.

As shown in FIGS. 2 and 3, the evaporator 60 comprises an upright thermally insulated chamber or vessel having a lower cylindrical section 61 and an upper frustoconical section 62, widening in horizontal cross-section toward the top. The vessel 61-62 may be constructed with an outer steel or like shell 63 and an inner, appropriately thick lining 64 of inert insulating material such as dense alumina, is being understood that alternative structures, preferably embodying thermal insulation and avoiding materials that might be attacked by the gas, can be employed. At a central region, e.g. midway between bottom and top, of the vertical cylindrical portion 61, a thermally insulated screw feeder 66 advances powdered aluminum trichloride into the vessel from a source such as the hopper 67 at the entering end of the screw, which is driven by suitable means (not shown).

The screw device, preferably projecting somewhat into the column, delivers the pulverulent solid so as to fall in distributed form across a major portion, centrally, of the cross-section of the column. At the foot of the vessel,

heated aluminum trichloride gas enters through a pipe 68 and a distributing device such as the perforated plate 69 at the upwardly opening end of the pipe. Thus as the powder falls it is heated by radiation and convection from the upwardly passing gas, and is also uniformly dispersed by this rising flow of the hot gas. In consequence, the solid aluminum trichloride promptly sublimes into the gas stream, whereby a correspondingly larger amount of aluminum trichloride gas is discharged through the pipe 70 at the upper, closed end 71 of the chamber.

Not only is there an immediate and intimate association of the solid powder and the gas for correspondingly rapid volatilization of the solid, but the circumstances are such as to promote and complete the evaporation during the period of upward gas travel, while inhibiting and indeed effectively preventing any deposit of solids at the base of the column. Specifically, because the diameter of each particle decreases as it falls and because the gas velocity is greatest at the bottom of the column (by reason of the higher temperature and higher conversion of solid to gas), there is no possibility of solids falling to the bottom of the chamber, especially if the maximum particle size in the feed is appropriately controlled, e.g. preferably not larger than will pass 65 mesh (i.e. a screen of 65 openings to the linear inch) in the case of aluminum trichloride. It is conceivable to accommodate larger particle size powder but the column must then ordinarily be excessively or inconveniently long. Some fine solid material, either as introduced or as constituting traces of oxide formed, may travel upwardly with the gas stream, i.e. above the feeding device 66, but evaporation continues so that by the time the gas reaches the outlet 70, all of the sublimable solid has been converted to gas.

It will thus be seen that the evaporation procedure is both simple and efiicient, in that the aluminum trichloride powder is continuously fed into the rising column of heated gas, where under preferred conditions it is quickly and completely evaporated and carried olf as an augmented gas stream. It may therefore be said that the action is in effect instantaneous, and hence is aptly described as a flash evaporation. No solids accumulate any where in the evaporator, to interfere with heat transfer or otherwise to create operating or maintenance problems. While the upwardly flaring section 62 can be omitted in some cases, it is of advantage in insuring completeness of evaporation, by reducing the velocity to afford a slightly longer time of passage, while accommodating the increase in amount of gaseous aluminum trichloride, occasioned by progressive evaporation of the latter from the solid particles.

As utilized with a self-contained circuit for generating a continuing stream of trichloride gas, the system in FIG. 2 includes other instrumentalities which may be of conventional construction. Thus the discharged and augmented stream of gas from the pipe 70 is taken through a dust separator 74, which may be a cyclone or other suitable device, whereby solid residues, e.g. small quantities of fine aluminum oxide, may be withdrawn as indicated at 75. From the dust separator, the cleaned gas is carried as at 76 to be divided into a product flow 77 and a recirculating line 78. Specifically, an amount of gas corresponding to the quantity of solid aluminum trichloride (less the very slight loss by dust in the separator 74) is discharged through the line 77 for use as desired, while the remainder of gas is recirculated, with the pump 79 or equivalent means, in the line 78. The further path of recirculation includes a gas heater 80, of an appropriate design, from which the re-heated gaseous trichloride, departing at 81, is returned to the bottom inlet pipe 68 of the evaporator. Thus with the aid of a constant, circulating quantity of the trichloride in gaseous form, powder supplied to the hopper 67 is continuously evaporated and in effect discharged as gas through the line 77, for whatever use is desired. One suitable use, of course, is

8 in aluminum monochloride refining systems, where supplemental aluminum trichloride gas may be needed or where quantities of aluminum trichloride are continuously or intermittently condensed and are to be re-evaporated for repeated use in the refining of aluminum.

Another specific system is that of FIG. 1, where instead of separately heating a recirculated stream of gas, an appropriate quantity of suitably hot aluminum trichloride in gaseous state is withdrawn from the main path of circulation of the refining system.

As an example of an evaporator capable of receiving, say, 1200 pounds per hour of heated aluminum trichloride gas and of vaporizing an equal amount of solid material to yield a discharge flow, through the pipe 70, of approximately twice the gas input one embodiment of the equipment involved a chamber having a vertical cylindrical portion 61 nine feet tall and two feet in diameter, with an upper flaring portion 62 four feet high and four feet in diameter at its top, these being internal dimensions of the structure. As an instance of the process with such apparatus, 1200 pounds per hour of aluminum trichloride gas at 700 C. are introduced through the pipe 68, while 1200 pounds per hour of aluminum trichloride powder are delivered by the screw 66 and essentially completely vaporized by the upward flow of hot gas, the powder preferably having a particle size not larger than about mesh. The discharge through the pipe consists of 2400 pounds per hour of gaseous aluminum trichloride at, say, 300 C., it being understood that the outlet temperature of the gas is controlled by the relative proportions of cold solid and hot gas fed. After traversing the dust separator 74, product discharge of 1200 pounds per hour of aluminum trichloride gas, at 300 C., is obtained in the line 77; produced gas is thus bled off from the stream at a mass flow rate equivalent to the solid feed rate. The remaining gas is recirculated through the gas heater 80, here it is brought up to the selected temperature of 700 C., for repeated travel upwardly in the evaporator 60. It will be understood, of course, that other rates and temperature conditions may be employed, as governed by feed rates of materials and provision of sufficient heat for evaporation of the solid at its temperature of sublimation. For effective contact time, gas velocities in the column are very preferably kept below about five feet per second and are most preferably about three feet per second.

In order to provide relatively uniform gas flow across the columns, or across most of it, centrally thereof, suitable distribution means such as a perforated plate 69 are employed. For the above example of apparatus, a suitable plate 69 (FIGS. 2 and 3) may be of stainless steel, graphite, or other material, say one-fourth inch thick, and having a multiplicity of holes one-eighth inch in diameter, one arrangement of such holes, equally spaced, being: four holes at a one inch radius from the center of the plate, eight holes at a two inch radius, twelve at a three inch radius, sixteen at a four inch radius, and twenty at a five inch radius.

FIGS. 4 and 5 show a modified gas distributing arrangement, where the gas inlet pipe 84- (corresponding to the pipe 68) opens against a plate 85 supporting a plurality of tubes 85 which are secured vertically in corresponding openings in the plate, projecting both above and below it and thus constituting a nozzle assembly. As an example of a nozzle design appropriate for an evaporator dimensioned as indicated above, there may be eight tubes or pipes 86, each six inches long and having an inside diameter of one fourth inch, one of the pipes being disposed at the center and the others being arranged equally spaced on a circle diameter of fourteen inches.

Nozzle or distributing arrangements of this character are especially effective in delivering the gas in a uniform manner and most preferably with limited velocity as stated above, for travel upwardly in the column of the evaporator. It is usually desirable that the flow should 9 be essentially of laminar character, especially in that any large turbulence might tend to carry some particles of powder out of the vessel.

It will now be seen that the procedure and apparatus of the flash evaporating system, in the several figures, afford an especially advantageous way of converting solid aluminum trichloride to a gaseous state, with special cooperation by reason of the use of hot gas of the same solid as a heating agent. It should also be apparent that the improved procedure and apparatus are applicable to sublimation of other solid materials, especially where similar problems arise.

It is to be understood that the invention is not limited to the specific steps and devices herein disclosed but may be carried out in other ways without departure from its spirit.

We claim:

1. In procedure for subhalide refining of aluminum wherein gas containing normal aluminum halide is continuously circulated along a path which extends through a converting region, containing impure aluminum for producing aluminum monohalide, a monohalide decomposing region for depositing purified aluminum and a gas heating region and then again to the converting region, in succession, said gas consisting essentially of normal halide of aluminum as circulated from the decomposing region, through the heating region and into the converting region, the aforesaid procedure further including reacting said normal halide with aluminum of a charge of impure aluminum material at high temperature in said converting region to yield gaseous aluminum monohalide in the circulating gas while said charge material is advanced through said converting region countercurrent to the gas for progressive depletion of aluminum by said reaction to leave a high temperature residue of said charge material which moves along a discharge path from the converting region, to discharge therefrom: the process which comprises withdrawing a portion of the circulating gas at a locality in the gas path intermediate the decomposing region and the heating region, cooling said withdrawn gas to condense the normal halide therein to a nongaseous state while separating gaseous impurities, evaporating said. condensed halide to yield gaseous normal halide having a substantially lower temperature than both said residue and the circulating gas which passes from the heating region to the converting region, and restoring said last-mentioned lower temperature evaporated gaseous halide to the circulating stream by conducting it into the aforesaid discharge path from the converting region, for heat exchange with the charge residue to cool the latter while augmenting the sup-ply of heated gaseous halide for the converting region.

2. Procedure as defined in claim 1, wherein the evaporated gaseous halide is established at a temperature substantially lower than the circulating gas at the aforesaid locality of withdrawal, and which includes withdrawing a further quantity of the circulating gas from a locality between the decomposing region and the heating region, said last-mentioned further withdrawn quantity of gas having a temperature which is substantially higher than said evaporated gaseous halide and substantially lower than the temperature of gas passing from the gas heating region to the converting region, and supplying said lastmentioned further withdrawn quantity of gas to the circulating stream by conducting it into the aforesaid discharge path at a place in the latter between the converting region and the place of introduction of the evaporated gaseous halide, so that the charge residue moves along said path countercurrently to successive re-introduced streams of gaseous halide of successively lower temperature.

3. In procedure for subhalide refining of aluminum wherein gas containing normal aluminum halide is continuously advanced along a path which extends into and through a heated converting region containing impure aluminum for reaction of said normal halide to produce gaseous aluminum monohalide and then through and out of a monohalide decomposing region, for depositing puritied aluminum, said gas consisting essentially of normal halide of aluminum as it enters the converting region and as it leaves the decomposing region, the process which comprises withdrawing a portion of the halide gas from said path downstream of the decomposing region, cooling said withdrawn gas to condense the normal halide therein to a non-gaseous state while separating gaseous impurities, evaporating said condensed halide by supplying thereto another portion of gaseous normal halide withdrawn from the said path at a locality downstream of the decomposing region and efiectuating said evaporation with heat of said last-mentioned withdrawn portion, while exposing said condensed halide to said last-mentioned gaseous portion, to yield a continuing quantity of gaseous normal halide including said last mentioned evaporated halide, and restoring said last-mentioned quantity of gaseous halide to the aforesaid path for traversal of the converting region.

4. In procedure for subhalide refining of aluminum wherein gas containing aluminum trichloride is continuously circulated along a path which extends through a converting region, containing impure aluminum for producing aluminum monochloride, a monochloride decomposing region for depositing purified aluminum and a gas heating region and then again to the converting region, in succession, said gas consisting essentially of aluminum trichloride as circulated from the decomposing region, through the heating region and into the converting region, the aforesaid procedure further including reacting said aluminum trichloride with aluminum of a charge of impure aluminum material at high temperature in said converting region to yield gaseous aluminum monochloride in the circulating gas while said charge material is advanced through said converting region countercurrent to the gas for progressive depletion of aluminum by said reaction, to leave a high temperature residue of said charge material which moves along a discharge path from the converting region, to discharge therefrom: the process which comprises Withdrawing a portion of the circulating gas at a locality in the gas path intermediate the decomposing region and the heating region, cooling said withdrawn gas to condense the aluminum trichloride therein to a solid state while separating gaseous impurities, evaporating said condensed solid trichloride by supplying to said solid trichloride in divided form, a portion of hot gaseous aluminum trichloride withdrawn from the circulating stream at a locality downstream of the decomposing region, to yield a quantity of gaseous aluminum trichloride having a substantially lower temperature than said residue and the circulating gas which passes from the heating region to the converting region, and restoring said last-mentioned lower-temperature evaporated gaseous trichloride to the circulating stream by conducting it into the aforesaid path discharge path from the converting region, for heat exchange with the charge residue to cool the latter while augmenting the supply of heated gaseous aluminum trichloride for the converting region.

5. Procedure as defined in claim 4, wherein the evaporated gaseous trichloride is established at a temperature substantially lower than the circulating gas at the aforesaid locality of withdrawal, and which includes withdrawing a further quantity of the circulating gas from a locality between the decomposing region and the heating region, said last-mentioned further withdrawn quantity of gas having a temperature which is substantially higher than said evaporated gaseous trichloride and substantially lower than the temperature of gas passing from the gas heating region to the converting region, and supplying said last-mentioned further withdrawn quantity of gas to the circulating stream by conducting it into the aforesaid discharge path at a place in the latter between the converting region and the place of introduction of the evaporated 1 1 gaseous trichloride, so that the charge residue moves along said path countercurrently to successive reintroduced streams of gaseous trichloride of successively lower temperature.

6. In procedure for subhalide refining of aluminum wherein gas containing aluminum trichloride is continuously circulated along a path which extends through a converting region, containing impure aluminum for producing aluminum monoehloride, a monochloride decomposing region for depositing purified aluminum and a gas heating region and then again to the converting region, in succession, said gas consisting essentially of aluminum trichloride as circulated from the decomposing region, through the heating region and into the converting region, the aforesaid procedure further including reacting said aluminum trichloride with aluminum of a charge of impure aluminum material at high temperature in said converting region to yield gaseous aluminum monochloride in the circulating gas while said charge material is advanced through said converting region countercurrent to the gas for progressive depletion of aluminum by said reaction, to leave a high temperature residue of said charge material which moves along a discharge path from the converting region, to discharge therefrom: the process which comprises continuously withdrawing a portion of the circulating gas at a locality in the gas path intermediate the decomposing region and the heating region, cooling said withdrawn gas to condense the aluminum trichloride therein to a non-gaseous state while separating gaseous impurities, continuously transferring said condensed trichloride to an evaporating region. continuously evaporating said condensed trichloride in said region to yield a continuing quantity of gaseous aluminum trichloride having a lower temperature than the circulating gas which passes from the decomposing region to the heating region, and restoring said last-mentioned lower-temperature evaporated gaseous trichloride to the circulating stream by con ducting it into the aforesaid discharge path from the converting region for heat exchange with the charge residue to cool the latter while augmenting the supply of heated gaseous aluminum trichloride for the converting region.

'7. Procedure as defined in claim 6, in which the condensed aluminum trichloride is established in divided solid form, and in which the evaporating step comprises withdrawing a further portion of the hot circulating gas from a locality in the gas path between the decomposing region and the heating region, advancing said last-mentioned portion of gas through an evaporating region while feeding the divided solid aluminum trichloride into said region at a central locality thereof for dispersion in said last-mentioned gas to be evaporated by the heat of said gas, and withdrawing an augmented flow of aluminum trichloride gas from said region, to constitute the evaporated gas conducted to the discharge path.

8. In procedure for subhalide refining of aluminum wherein gas containing aluminum trichloride is continuously circulated along a path which extends through a converting region, containing impure aluminum for producing aluminum monoehloride, a monochloride decomposing region for depositing purified aluminum and a gas heating region and then again to the converting region, in succession, said gas consisting essentially of aluminum trichloride as eirculated from the decomposing region, through the heating region and into the converting region, the process which comprises withdrawing a portion of the circulating gas at a locality in the gas path intermediate the decomposing region and the heating region, cooling said withdrawn gas to condense the aluminum trichloride therein to a solid state while separating gaseous impurities, continuously withdrawing another portion of hot gaseous aluminum trichloride from the circulating stream at a locality in the gas path between the decomposing and heating regions, evaporating said condensed solid alumnum trichloride by feeding it, in divided form, into an evaporating region while passing through said last-mentioned region the last-mentioned portion of hot gaseous trichloride, to yield a continuing quantity of gaseous aluminum trichloride comprising the evaporated trichloride and the last-mentioned withdrawn trichloride, and restoring said last-mentioned continuing quantity of gaseous trichloride to the circulating stream.

9. In procedure for subhalide refining of aluminum wherein gas containing normal aluminum halide is continuously circulated through a converting region, containing impure aluminum for producing aluminum monohalide, a monohalide decomposing region for depositing purified aluminum and a gas heating region and then again to the converting region, in succession, said gas comprising normal halide of aluminum as circulated through the heating region and into the converting region, the aforesaid procedure further including reacting said normal halide with aluminum of a quantity of impure aluminum in said converting region at a temperature of at least about 1000 C. to yield gaseous aluminum monohalide in the circulating gas while discharging high temperature residue from the converting region through a discharge region, and the aforesaid procedure also including decomposing said subhalide to yield purified aluminum and normal halide in the decomposing region, the gas leaving said decomposing region having an elevated temperature of less than 800 C., and the gas traversing the heating region being there heated to a temperature of at least about 1000 C.: the process which comprises withdrawing a minor portion of the circulating gas at a locality intermediate the decomposing region and the heating region, cooling said withdrawn gas to condense the normal halide therein to a non-gaseous state while separating gaseous impurities, evaporating said condensed halide by heat exchange with and exposure to some gas of that which is circulating from the decomposing region to the converting region, to convert said condensed halide to gaseous form and directing said last-mentioned evaporated gaseous halide to a locality of the discharge region for heat exchange with the residue of the reaction and for travel to the converting region to augment the supply of halide for the reaction.

10. A process as defined in claim 9, wherein the withdrawn halide gas is condensed in the form of a pulverulent solid, and wherein the evaporation of said solid comprises bringing said solid into contact with a stream of the gas from the main circulating gas, for rapid conversion of the solid to gaseous form, to produce said evaporated gaseous halide having a temperature below about 400 C.

11. A process as defined in claim 10, wherein the gas from the decomposing region has a temperature of about 700 C. and is employed at said temperature for the evaporation of the condensed, pulverulent halide, to yield a gaseous flow for cooling the converting region residue, which gaseous flow has a temperature of about 300 C.

12. A process as defined in claim 9, wherein another minor portion of the circulating halide gas is withdrawn at a locality upstream of the heating region in the path of gas flow from the decomposing region to said heating region, said last-mentioned portion, at a temperature of 600 C.800 C., being directed to a locality of the discharge region which lies between the converting region and the first-mentioned locality of the discharge region for heat exchange with the discharging residue preliminarily to its heat exchange with the gas produced from the condensed halide.

13. In procedure for subhalide refining of aluminum wherein gas containing aluminum trichloride is continuously passed into and through a converting region for converting aluminum of impure aluminum material into gaseous aluminum monochloride and monoehloridecontaining gas from said region is continuously passed into and through a monochloride-decomposing region for decomposing said monochloride to aluminum and gaseous aluminum trichloride, said gas consisting essentially of aluminum trichloride as passed into the converting region and as passed out of the decomposing region, the aforesaid procedure further including reacting said aluminum trichloride with aluminum of a charge of impure aluminum material in said converting region to yield the aforesaid gaseous monochloride while supplying heat to said charge and maintaining a high temperature in said converting region and While said charge material is advanced through said converting region countercurrent to the gas for progressive depletion of aluminum by said reaction, to leave a high tempera ture residue of said charge material which moves along a discharge path from the converting region, to discharge therefrom, and the aforesaid procedure also including restoring aluminum trichloride discharged from the decomposing region into the converting region, said restoring step including advancing aluminum trichloride in gaseous form through a gas-heating region for raising said gas to a high temperature and passing said lastmentioned high temperature aluminum trichloride gas into the converting region, said decomposing step discharging hot aluminum trichloride gas which is at a substantially lower temperature than the temperature of the converting region: the process which comprises continuously condensing aluminum trichloride gas discharged from the decomposing region to yield a continuing supply of non-gaseous aluminum trichloride while separating gaseous impurities, and continuously advancing said condensed trichloride to a trichlorideevaporating region for continuously vaporizing said nongaseous trichloride to yield a continuing flow of gaseous trichloride having a substantially lower temperature than the gas discharged from the decomposing region, and supplying said last-mentioned flow of gaseous trichloride to the aforesaid discharge path from the converting region at a locality separated in the course of movement of the charge residue from the place of introduction of high temperature trichloride gas into the converting region, for travel of said flow of gaseous trichloride along said discharge path into the converting region for heat exchange wth the charge residue to cool the latter while absorbing heat from said residue and augmenting the supply of heated gaseous trichloride into the converting region.

14. In apparatus for subhalide refining of aluminum, in combination, a refining system comprising a converter having a chamber arranged to receive aluminum-containing charge material and having gas inlet and outlet means at opposite ends of the chamber, for passage of halide gas to react with aluminum of the charge material, means associated with the converter for heating charge material in said chamber at localities between said inlet and outlet means, said converter being arranged for traversal of the chamber by charge material countercurrent to the gas and having means at the end of the chamber which has the gas outlet means, for admitting successive quantities of charge material into the chamber and means including enclosed structure communicating with the chamber at the end which has the gas inlet means, for providing a path for hot residue discharge beyond the gas inlet in the direction of travel of the charge material from the admitting means therefor, a decomposer connected with the outlet of the converter and arranged to receive reacted gas therefrom, for depositing aluminum metal and discharging halide gas, gas heating means, and means, including conduit structure associated with said decomposer, heating means and converter, for recirculating halide gas from the decomposer through the heating means to the inlet of the converter, a halide condenser connected to said recirculating means to receive a part of the gas from the decomposer, for condensing solid halide and discharging non-condensable gas, an evaporating vessel, means for conducting a portion of heated halide gas away from the conduit structure at a locality between the decomposer and the heating means, and for directing said heated gas upwardly in the vessel, means, connected to the condenser to receive solid halide from the condenser, for feeding solid halide in divided form into the stream of halide gas in said vessel, for evaporation of said last-mentioned solid halide by the heat of said last-mentioned gas, and means connected with an upper part of said vessel and with said residue discharge path means of the converter at a locality of said discharge path means which is spaced from the aforesaid gas inlet means in the direction of travel of discharging residue, for conducting gaseous halide, including the evaporated halide, from the vessel to the residue discharge path means of the converter, for passage of said gas through the discharging hot residue into the converter.

15. Procedure for evaporating aluminum trichloride, comprising conveying a stream of hot aluminum trichloride gas from a source thereof, and directing solid aluminum trichloride in finely divided particulate form along a path separate from said gas source and then into said stream of hot aluminum trichloride gas, and thereby dispersing said particulate solid aluminum trichloride in said gas and evaporating such last-mentioned aluminum trichloride by the heat of said gas.

16. Procedure for evaporating aluminum trichloride, comprising establishing a flow of hot aluminum trichloride gas at a first region, conducting said flow of hot aluminum trichloride gas from said first region to and through a second region while feeding into only said second region, into said flow of gas therein, material consisting entirely of finely divided solid matter and comprising discrete, fine, solid particles of aluminum trichloride, and thereby dispersing said particles of aluminum trichloride in said gas and evaporating aluminum trichloride of said particles by the heat of said gas, and

withdrawing an augmented flow of aluminum trichloride gas from said second region.

References Cited by the Examiner UNITED STATES PATENTS 1,518,126 12/24 Reed 23-294 1,837,199 12/31 Brode 2392 2,376,045 5/45 Gaither 23-294 2,526,564 10/50 Hepp et al. 2396 2,564,337 8/51 Maddex -63 X 2,705,186 3/55 Hardy et al. 2396 2,797,981 7/57 Tooke 2396 2,877,106 3/59 Aspegren 75-34 2,914,398 11/59 Johnston et al. 75-68 2,937,082 5/60 Johnston et al, 75-68 3,078,159 2/63 Hallingshead et al. 75-68 X FOREIGN PATENTS 342,208 1/ 31 Great Britain.

BENJAMIN HENKIN, Primary Examiner.

DAVID L. RECK, Examiner, 

1. IN PROCEDURE FOR SUBHALIDE REFINING OF ALUMINUM WHEREIN GAS CONTAINING NORMAL ALUMINUM HALIDE IS CONTINUOUSLY CIRCULATED ALONG A PATH WHICH EXTENDS THROUGH A CONVERTING REGION, CONTAINING IMPURE ALUMINUM FOR PRODUCING ALUMINUM MONOHALIDE, A MONOHALIDE DECOMPOSING REGION FOR DEPOSITING PURIFIED ALUMINUM AND A GAS HEATING REGION AND THEN AGAIN TO THE CONVERTING REGION, IN SUCCESSION, SAID GAS CONSISTING ESSENTAILLY OF NORMAL HALIDE OF ALUMINUM AS CIRCULATED FROMTHE DECOMPOSING REGION, THROUGH THE HEATING REGION AND INTO THE CONVERTING REGION, THE AFORESAID PROCEDURE FURTHER INCLUDING REACTING SAID NORMAL HALIDE WITH ALUMINUM OF A CHARGE OF IMPURE ALUMINUM MATERIAL A THIGH TEMPERATURE IN SAID CONVERTING REGION TO YIELD GASEOUS ALUMINUMMONOHALIDE IN THE CIRUCLATING GAS WHILE SAID CHARGE MATERIAL IS ADVANCED THROUGH SAID CONVERTING REGION COUNTERCURRENT TO THE GAS FOR PROGRESSIVE DEPLETION OF ALUMINUM BY SAID REACTION TO LEAVE A HIGH TEMPERAURE RESIDUE OF SAID CHARGE MATERIAL WHICH MOVES ALONG A DISCHARGE PATH FROM THE CONVERTING REGION, TO DISCHARGE THEREFROM: THE PROCESS WHICH COMPRISES WITHDRAWING A PORTIN OF THE CURCULATING GAS AT A LOCALITY IN THE GAS PATH INTERMEDIATE THE DECOMPOSING REGION AND THE HEATING REGION, COOLING SAID WITHDRAWN GAS TO CONDENSE THE NORMAL HALIDE THERIN TO A NONGASEOUS STATE WHILE SEPARATING GAGEOUS IMPURITEIS, EVAPO- 